On the fly image resizing with image_filter

nginx_image_filter.conf

# On the fly resizing of images inside /images/*/
# based on query string "width" and "height" parameters

location ~ /images/(.+)/ {
  set $width -;
  set $height -;
  set $entity $1;

  if ($arg_width) {
    set $width $arg_width;
  }

  if ($arg_height) {
    set $height $arg_height;
  }

  image_filter resize $width $height;
  image_filter_buffer 128M;

  random_index on;

  if (!-e $request_filename) {
    rewrite ^ /images/$entity/;
  }
}